High-sulfur steel for automobile wheel hub and preparation method thereof

Abstract

The present invention relates to a high-sulfur steel for automobile wheels and a preparation method thereof. The preparation method comprises converter smelting (preliminary smelting is carried out in a converter using a fixed amount of non-desulfurized molten iron and high-quality scrap steel as raw materials. During tapping, silicon manganese and high-carbon ferromanganese are added in sequence. According to the sulfur content of the molten steel at the converter end point, ferrosulfur is added during the tapping process to adjust the sulfur content), LF refining, continuous casting, and steel rolling. The high-sulfur steel for automobile wheels produced by the present invention does not require the separate addition of Mo and a large amount of Ti, thereby saving a large amount of cost. While having good cutting performance, the steel needs to have excellent toughness to maintain component stability. The mechanical properties in the hot-rolled state can meet the following requirements: tensile strength ≥735 MPa, lower yield strength ≥420 MPa, elongation ≥16%, and hot-rolled hardness between 210 and 240 HB.

Description

Technical Field

[0001] The present invention relates to the field of automobile steel manufacturing, and in particular to high-sulfur steel for automobile wheel hubs and a preparation method thereof. Background Art

[0002] The wheel hub is a crucial component of a vehicle and a crucial element in its operation. It bears and transmits all forces and torques between the vehicle and the road. This directly impacts the vehicle's overall driving stability, safety, reliability, ride comfort, traction, and appearance. It also significantly impacts the vehicle's overall energy consumption and tire life. The wheel hub is also a crucial component of the vehicle's chassis system, transmitting forces and torques between the wheel and frame through the suspension system, stabilizing vehicle steering, and buffering the impact of road bumps on the frame or body. The vehicle's driving torque is ultimately transmitted to the wheel hub, driving the vehicle and ensuring smooth driving. The wheel hub bears the entire weight of the vehicle while also withstanding the alternating impact loads generated by the rotational torque. Wheel hub stability is crucial for vehicle safety, making wheel hub strength crucial. Currently, the main types of wheel hubs on the market are aluminum alloy and steel. The former offers advantages such as improved heat dissipation, tire protection, extended tire life, superior grip, and a high coefficient of friction. However, aluminum alloy wheels are expensive. Compared to steel wheels, which offer comparable performance to aluminum alloy wheels, steel wheels are significantly cheaper, offering considerable economic benefits. Currently, approximately 95% of vehicles worldwide use steel wheels. Improved machinability also makes it easier to create finished wheels with aesthetically pleasing appearances comparable to aluminum alloy wheels.

[0003] Based on the above reasons and considering the economic efficiency, it is urgent to design a steel for automobile wheel hub that has high uniformity, high strength and toughness, good machinability and sufficient strength. Summary of the Invention

[0004] In order to solve the above problems, the present invention discloses a high-sulfur steel for automobile wheel hub and a preparation method thereof. The specific technical solution is as follows:

[0005] A method for preparing high-sulfur steel for automobile wheel hubs comprises the following steps:

[0006] (1) Converter smelting:

[0007] Non-desulfurized hot metal and high-quality scrap steel are used as raw materials for primary smelting in a converter. When tapping, silicon manganese (FeMn 68 Si 18 ): 8.5~10.5kg / t, high carbon ferromanganese (FeMn 68 C 7.0): 13~15kg / t, according to the S content of the molten steel at the end of the converter, ferrosulfur is added during the tapping process to adjust the S content;

[0008] Before 20 tons of steel is tapped from the converter, aluminum cakes for pre-deoxidation are added to prevent alloy oxidation and waste. Alloys are added after 30 tons; the speed of adding alloys is controlled to ensure that all alloys are added to the ladle when the tapping amount reaches 1 / 2, and the bottom blowing argon stirring is adjusted to 500-600NL / min. After all the alloys are melted, 3 / 4 of the slag is added. At this time, the bottom blowing argon stirring time is controlled to 1min, and then the bottom blowing argon stirring is quickly adjusted to 200-300NL / min. Deoxidizer calcium aluminum iron is added to the impact area. After 1 minute of adding the deoxidizer, the argon stirring is adjusted to 100-200NL / min, and the remaining 1 / 4 of the slag is added to the ladle; after the slag is added, it is soft-blown at the argon blowing station for 2-3 minutes, and aluminum wire is fed into the molten steel. 100m of aluminum wire with a specification of φ9mm is fed into the first furnace of the tundish, and 70m of aluminum wire with a specification of φ9mm is fed into the continuous casting furnace.

[0009] (2) LF refining:

[0010] 2.1) In the early stage of LF refining and when adjusting the composition, use argon blowing and stirring (preferably without excessive molten steel overturning or exposure) to homogenize the composition. Otherwise, maintain soft argon blowing. The bottom blowing stirring flow rate during the refining process is less than 600NL / min.

[0011] 2.2) Slag Adjustment: In principle, no additional slag is added during the LF refining process, and no desulfurization is performed intentionally. If the sulfur content of the first batch of molten steel in LF refining is too low, ferrosulfur is added to adjust the sulfur content. The refining slag must have good fluidity and the white slag time must be ≥25 minutes.

[0012] 2.3) Use silicon carbide, calcium carbide, and aluminum particles to deoxidize the slag surface. The amount of calcium carbide added is 40-60 kg / furnace, and the amount of silicon carbide added is 100-120 kg / furnace. The Al content of the second sample is controlled to be 0.010%-0.015%;

[0013] 2.4) Use high carbon ferrochrome to adjust the Cr content in refining; in the case of white slag in the later stage of refining, use ferrotitanium to adjust the Ti content;

[0014] 2.5) No denaturation treatment is performed, and the sulfur content is adjusted to the internal control range by feeding the sulfur line at the end of LF refining;

[0015] 2.6) Soft blowing for 20 to 30 minutes;

[0016] 2.7) During the refining process, the requirements for bottom blowing argon stirring are as follows: when adding alloys to adjust the chemical composition, the bottom blowing argon flow rate is controlled at 400-500 NL / min, and the slag surface blowing area is controlled at 100-200 mm; during other refining times, the bottom blowing argon flow rate is controlled at 100-200 NL / min, and the molten steel is not exposed when the slag surface moves slightly. The bottom blowing argon flow rate is prohibited to exceed 200 NL / min;

[0017] (3) Continuous casting:

[0018] The superheat of the first ladle is 25-45℃, and the casting speed is 1.20m / min; the superheat of the continuous casting furnace is 20-30℃, and the casting speed is 1.35m / min. The temperature drop of each ladle of molten steel from the beginning to the end of casting is ≤5℃;

[0019] (4) Steel rolling:

[0020] The continuous casting billet is cold charged into the furnace, and the walking-beam heating furnace is re-divided into six heating zones from the original three heating zones; the temperature of the preheating section is ≤850℃, the temperature of the first heating section is 950±10℃, the temperature of the second heating section is 1100±10℃, the temperature of the third heating section is 1140±10℃, the temperature of the first soaking section is 1160±10℃, and the temperature of the second soaking section is 1150±10℃. From the perspective of the division of heating areas, the preheating section, the first heating section, and the second heating section are the billet uniform heating sections; the third heating section, the first soaking section, and the second soaking section are the billet homogenization and high-temperature diffusion stages; the starting rolling temperature is ≥1050℃, the finishing rolling temperature is ≥950℃, the upper cooling bed temperature is ≥850℃, the slow cooling temperature of the steel entering the pit is ≥430℃, the slow cooling time of the steel entering the pit must be ≥72h, and the surface temperature of the steel is ≤100℃ when the steel is out of the pit and out of the pit.

[0021] Furthermore, the chemical composition and mass content of the molten steel in step (1) are as follows: C: 0.40% to 0.43%, Mn: 1.57% to 1.65%, Cr: 0.12% to 0.15%, Ti: 0.02% to 0.03%; there is no need to add Mo and a large amount of Ti elements separately, As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, and Bi≤0.0005%.

[0022] Furthermore, in step (1), in order to prevent the molten steel from being over-oxidized, a high carbon drawing operation is adopted at the end of the converter, so that the mass content of C is ≥0.08%, the tapping temperature is 1620-1670°C, and the mass content of phosphorus is ≤0.012% when tapping.

[0023] Furthermore, in the step (1), when the converter is tapping steel, aluminum blocks are added for precipitation deoxidation according to the oxygen determination result at the blowing end point.

[0024] The slag material is made by using lime, refined slag and quartz sand, with the amount of lime added being 500 kg / furnace, the amount of refined slag added being 200 kg / furnace and the amount of quartz sand added being 100 kg / furnace.

[0025] Furthermore, in the step (2), argon blowing is used for stirring in the early stage of refining and when adjusting the composition. The intensity of the stirring and blowing argon is suitable to ensure that the molten steel is not greatly stirred and exposed, and the composition is uniform. Otherwise, the argon blowing is maintained soft, and the bottom blowing stirring flow rate during the refining process is less than 600NL / min.

[0026] Furthermore, in step (2), the temperature of the first ladle is 1557-1577°C, the temperature of the ladle in the continuous casting furnace is 1537-1567°C, the overheating degree of the first ladle is 25-45°C, and the overheating degree of the continuous casting furnace is 20-30°C.

[0027] Furthermore, in the step (3), billet casting is carried out in an arc continuous casting machine, the billet specification is 210*210mm, a tundish covering agent and a crystallizer protective slag are used, and 100% protective casting is implemented throughout the whole process to avoid secondary oxidation of the molten steel.

[0028] Furthermore, in step (3), the flow rate of cold water is controlled at 120±5m 3 / h, the M-EMS electromagnetic stirring current is 350A, the frequency is 2.5Hz, and the F-EMS electromagnetic stirring current is 250A, the frequency is 10Hz.

[0029] Furthermore, in step (4), the 210*210 mm square continuous casting billet is cold-charged into the furnace, and the total heating time is controlled within 2.5 to 3.0 h, of which the high-temperature diffusion time is 1.25 to 1.5 h.

[0030] A high-sulfur steel for automobile wheel hubs is produced by the above-mentioned method for producing high-sulfur steel for automobile wheel hubs. The high-sulfur steel for automobile wheel hubs comprises, in order by mass percentage, the following elements: C: 0.40%-0.43%, Si: 0.25%-0.33%, Mn: 1.57%-1.65%, Cr: 0.12%-0.15%, Ti: 0.02%-0.03%, P≤0.012%, S: 0.095%-0.11%, Cu≤0.05%, Ni≤0.04%, As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, Bi≤0.0005%, and the balance being Fe and unavoidable impurity elements.

[0031] The beneficial effects of the present invention are:

[0032] (1) The present invention provides a high-sulfur steel for automobile wheel hubs and a preparation method thereof. After fully considering the requirements for the mechanical properties of the steel, the amount of precious alloy Ti iron added is reduced by increasing the C and Mn contents and adding appropriate Cr elements, and no longer adding Mo iron separately. This can significantly reduce production costs and smelting difficulty. According to calculations, the cost can be reduced by 200 yuan per ton of steel.

[0033] (2) This invention takes into account the "hot brittleness" of medium-carbon, high-sulfur steel and the impact of large amounts of sulfides on the continuity of the steel, while also meeting the mechanical performance requirements of automotive wheels. Meeting all three of these conditions simultaneously is somewhat challenging, and the chemical composition and process were redesigned with these considerations in mind.

[0034] (3) The high-sulfur steel for automobile wheel hubs of the present invention has a tendency to grow grains during high-temperature heating. Therefore, elements for controlling high-temperature grain growth must be added to the high-sulfur steel for automobile wheel hubs of the present invention. Considering the presence of a certain amount of nitrogen in the molten steel and cost considerations, a certain amount of titanium is added to the steel of the present invention to form TiN, which can prevent grain growth and thus achieve the effect of grain refinement and strengthening. In order to control the size of the titanium nitride inclusions formed, the Ti content is determined to be 0.02% to 0.03%.

[0035] (4) The present invention strictly controls the residual element content of molten iron, selects high-quality scrap steel for smelting, optimizes the smelting process to achieve ultra-low control of five harmful elements: As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, and Bi≤0.0005%, thereby ensuring the stability of the processed automobile wheel hub.

[0036] (5) The method for preparing high-sulfur steel for automobile wheel hubs of the present invention eliminates the need for desulfurization of molten iron, effectively reducing production costs. The inherent advantage of uniform sulfur dispersion in high-sulfur molten iron is fully utilized, thereby improving the uniform distribution of sulfide in the steel and ensuring uniform mechanical properties.

[0037] (6) The method for preparing high-sulfur steel for automobile wheel hubs of the present invention utilizes a six-stage ultra-precise temperature-controlled heating furnace for high-temperature heating, so that the original continuous casting billet is evenly heated on all four sides to prevent the formation of "yin-yang" surfaces, thereby improving the homogenization effect of the continuous casting billet and achieving a uniform rolling deformation rate, thereby preventing the formation of "split" defects during the rolling process. During the slow cooling process, the temperature drop rate is consistent, the microstructure transformation is uniform, and the product performance uniformity is effectively stabilized.

[0038] (7) The high-sulfur steel for automobile wheel hubs and its preparation method of the present invention optimize the superheat and casting speed parameters in the continuous casting process, improve the core structure of the ingot, use a large compression ratio to produce materials to increase the density of the steel, and ensure that ultrasonic flaw detection can reach the AA level.

[0039] (8) The method for preparing high-sulfur steel for automobile wheel hubs of the present invention optimizes the cooling intensity of the first and second cooling water during continuous casting, slows down the growth of columnar crystals, increases the equiaxed crystal ratio, and improves the uniformity of the composition of the entire cross-section of the ingot.

[0040] (9) The method for preparing high-sulfur steel for automobile wheel hubs of the present invention develops a new head-end electromagnetic stirring process to interrupt the growth of dendrites and make the steel liquid composition at the dendrite position as balanced as possible.

[0041] (10) The preparation method of the high sulfur steel for automobile wheel hub of the present invention has the following characteristics: the tensile strength of the steel is ≥735 MPa, the lower yield strength is ≥420 MPa, the elongation is ≥16%, and the hot rolling hardness is between 210 and 240 HB. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0043] Existing high-sulfur automotive wheel steel manufacturers add Mo and large amounts of Ti to the traditional main element control to improve the steel's hardenability and ensure mechanical properties in the hot-rolled state. The addition of precious alloys significantly increases production costs, which is disadvantageous for steel mills. The advantage of adopting a die-casting steelmaking method is that it eliminates the problem of condensation in the submerged nozzle, allowing for a smoother casting process and improving steel density, thereby increasing the flaw detection pass rate. The yield rate of die-cast ingots is only around 80%, while the yield rate of continuous-cast billets can reach approximately 95%, significantly improving economic efficiency. By redesigning the chemical composition to meet the mechanical property requirements of the steel in the hot-rolled state and rationally optimizing the continuous casting process, the density of the continuous-cast billets can be increased. Increasing the compression ratio from the continuous-cast billet to steel further increases the density of the steel, ultimately achieving the same flaw detection pass rate as die-cast materials.

[0044] Sulfur is a detrimental element in standard steel products. Its presence can cause hot brittleness and affect its performance, so the lower its content in standard steel, the better. However, many downstream users of special steel products require cutting to produce a variety of parts. While it's well known that sulfur, while affecting steel properties, can also significantly improve cutting performance, a certain amount of sulfur in special steel not only makes it easier to machine but also significantly reduces the life of cutting bits. In other words, a certain amount of sulfur in special steel allows the same cutting bit to produce more finished parts. This significantly improves production efficiency for downstream users, saves a certain amount of cutting bits, and reduces production costs, bringing significant benefits to the company. Steel mill development experience suggests that higher sulfur content in special steels generally improves cutting performance. However, there are currently no specific values ​​to measure the impact of sulfur content on cutting performance, and this can only be verified through downstream user experience. Therefore, the challenge in developing special steels lies in ensuring both cutting performance and meeting part requirements. Designing a composition that perfectly matches these two properties (cutting performance and other steel properties) is crucial.

[0045] To address the shortcomings of existing high-sulfur steel for automotive wheels, the chemical composition design, while fully considering the strength requirements of automotive wheels, strictly controls the carbon content. While aligning with production methods, this breaks with conventional chemical composition design thinking and innovatively introduces high carbon, high manganese, low chromium, and low titanium design requirements. The five harmful elements (As, Sn, Pb, Sb, and Bi) in the steel are strictly controlled to stabilize the steel's performance. A rational steelmaking process is designed to improve the uniformity of the molten steel's composition and reduce chemical segregation during solidification. A rational heating system for rolling further enhances the homogenization of the steel through high-temperature diffusion. Controlled heating temperature, starting rolling temperature, finishing rolling temperature, and slow cooling temperature ensure that the mechanical properties of the hot-rolled steel meet standard requirements.

[0046] The high-sulfur steel for automobile wheel hubs of the present invention has high uniformity and high strength and toughness. The processing of automobile wheel hubs with the steel of the present invention is relatively simple and greatly improves the efficiency of turning processing. The production process is simple to operate, the production cost is low, and the adaptability is strong. It can be promoted and used in this industry.

[0047] The high-sulfur steel for automobile wheel hubs of the present invention comprises the following elements in order by mass percentage: C: 0.40% to 0.43%, Si: 0.25% to 0.33%, Mn: 1.57% to 1.65%, Cr: 0.12% to 0.15%, Ti: 0.02% to 0.03%, P≤0.012%, S: 0.095% to 0.11%, Cu≤0.05%, Ni≤0.04%, As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, Bi≤0.0005%, and the balance is Fe and unavoidable impurity elements.

[0048] The following specifically describes the reasons for designing the chemical composition of high-sulfur steel for automobile wheels in the present invention:

[0049] C: The interplay between carbon and the strength and toughness of metallic materials necessitates careful consideration of the carbon content. Previous research indicates that increasing carbon rapidly increases the carbon equivalent of steel, significantly improving strength but significantly decreasing toughness. This reduces the steel's impact resistance, negatively impacting component life. Lower carbon levels do not improve the steel's mechanical properties. While alloying the molten steel can improve mechanical properties, this can significantly increase steelmaking costs. To maintain an optimal carbon content range while maintaining strength and good toughness, the carbon content is designed to be between 0.40% and 0.43%.

[0050] Si: Silicon can increase yield strength and improve steel's hardenability, tempering stability, and oxidation resistance. However, excessive silicon content can lead to severe surface decarburization and increase the steel's brittle transition temperature. Taking into account the impact of silicon on steel properties, the Si content is set at 0.25% to 0.33% during composition design.

[0051] Mn: Considering that when the Mn content is lower than 1.8%, as its content increases, it has a beneficial effect on strength and toughness, manganese is added as a particularly important alloying element. Therefore, the Mn content is determined to be 1.57% to 1.65%.

[0052] Ti: Considering the heating temperature characteristics of the production process, steel tends to grow grains during high-temperature heating. Therefore, an element must be added to the invention steel to control this high-temperature grain growth. Considering that molten steel typically contains a certain amount of nitrogen and considering cost considerations, a certain amount of titanium is added to this patented steel to form TiN, which inhibits grain growth and thus achieves grain refinement and strengthening. To control the size of the titanium nitride inclusions formed, the Ti content is set at 0.02% to 0.03%.

[0053] Cr: In order to compensate for the lack of strength in the low-carbon composition design, the steel of the present invention adds an appropriate amount of chromium element in the composition design, and the Cr content is determined to be 0.12% to 0.15%.

[0054] P: In view of the high requirements for hot-rolled mechanical properties of the invented steel, comprehensive consideration of smelting costs and prevention of cold brittleness, phosphorus is controlled as a harmful residual element, and the P content is determined to be ≤0.012%.

[0055] S: In order to improve the turning performance of automobile wheels, sulfur is appropriately added to the inventive steel. Considering good turning performance, the S content is determined to be 0.095% to 0.11%.

[0056] In order to ensure the stability of the processed automobile wheels, the five harmful elements in the steel are ultra-low controlled to As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, and Bi≤0.0005%.

[0057] Take 5 furnaces as an example to illustrate the application process:

[0058] In actual production, the following production process is used:

[0059] (1) The molten iron is not subjected to KR quantitative desulfurization treatment:

[0060] According to the requirements of the steel grade usage, this steel needs to have good machinability, so the steel must contain a higher sulfur content. The blast furnace molten iron does not need desulfurization treatment, which can reduce one process and reduce production costs compared with normal steel grades.

[0061] (2) Converter smelting:

[0062] High-quality non-desulfurized hot metal and high-quality scrap steel (the hot metal mass can be 80% and the high-quality scrap steel mass can be 20%) are used as raw materials for primary smelting in a converter. In order to prevent the molten steel from being over-oxidized, a high-carbon pulling operation is used at the converter end point (the high-carbon pulling operation is to increase the carbon content of the charged molten steel at tapping while ensuring the removal of harmful elements, so as to prevent the molten steel from being over-oxidized). When tapping, C: 0.11% to 0.13%, P: 0.008% to 0.011%, and the tapping temperature is 1640 to 1660°C. When tapping, aluminum blocks are added to the converter for precipitation deoxidation based on the oxygen determination results at the end of blowing. Lime, refined slag, and quartz sand are used for slag making. The lime is 500kg / furnace, the refined slag is 200kg / furnace, and the quartz sand is 100kg / furnace. When tapping, silicon manganese (FeMn 68 Si 18 ): 8.5~10.5kg / t, high carbon ferromanganese (FeMn 68 C 7.0): 13 ~ 15kg / t, according to the S content of the molten steel at the end of the converter, ferrosulfur is added during the tapping process to adjust the S content.

[0063] Aluminum cakes are added before 20 tons of steel is tapped from the converter, and alloys are added after 30 tons. The alloy addition rate is controlled to ensure that all the alloy is added to the ladle when the tapping volume reaches 1 / 2. At the same time, the bottom blowing argon stirring is adjusted to 550NL / min. After the alloy is completely melted, 3 / 4 of the slag is added. At this time, the bottom blowing argon stirring time is controlled at 1 minute. Then, the bottom blowing argon stirring is quickly adjusted to 250NL / min. The deoxidizer calcium aluminum iron is added to the impact area. After 1 minute of adding the deoxidizer, the argon stirring is adjusted to 150NL / min, and the remaining 1 / 4 of the slag is added to the ladle. After the slag is added, it is soft-blown at the argon blowing station for 2 to 3 minutes. Aluminum wire is fed into the molten steel, 100m for the first furnace of the tundish, and 70m for the continuous casting furnace.

[0064] Table 1 below shows the specific values ​​of the parameters of the converter tapping during the converter smelting operation and the soft blowing time after the slag is added in each embodiment.

[0065] Table 1

[0066]

[0067] (3) LF refining:

[0068] 1) In the early stage of refining and when adjusting the composition, adopt appropriate stirring and argon blowing intensity (so that the molten steel does not overturn or expose) to uniform the composition. Otherwise, maintain soft argon blowing. The bottom blowing stirring flow rate during the refining process is 500NL / min.

[0069] 2) Slag adjustment: No additional slag is added during the LF refining process, and the refined slag has good fluidity. The white slag time is 30 to 40 minutes.

[0070] 3) Deoxidize the slag surface using silicon carbide, calcium carbide, and aluminum granules. Add 40-60 kg of calcium carbide per furnace and 100-120 kg of silicon carbide per furnace. The Al content of the second sample is 0.011% to 0.015%.

[0071] When the molten steel enters the LF refining process, it is first sampled to detect the element content and convert the amount of alloy added. Based on the converted alloy amount, the molten steel is alloyed in the subsequent process, and the added alloy is evenly dissolved. After the alloying is completed, the molten steel is sampled for the second time to detect the content of each element in the molten steel. The mass content of Al in the second sample refers to the Al content detected during the second sampling of the molten steel after the molten steel is alloyed.

[0072] Table 2 shows the specific values ​​of the slag amount of slag surface deoxidation and the mass content of Al in the second sample in each embodiment in the LF refining operation.

[0073] Table 2

[0074]

[0075] 4) High carbon ferrochrome is used in refining to adjust the Cr content; in the case of white slag in the later stage of refining, ferrotitanium is used to adjust the Ti content, with a dosage of 0.55 kg / t.

[0076] 5) No denaturation treatment is performed. At the end of refining, the sulfur content is adjusted to the internal control range by feeding the sulfur line (the internal control range is the range that the company strictly controls based on the standard requirements, that is, higher than the standard requirements).

[0077] 6) The soft blowing time is 25 to 35 minutes.

[0078] 7) The temperature of the first bag is 1557~1577℃, and the temperature of the continuous casting furnace bag is 1537~1567℃.

[0079] During the refining process, the requirements for bottom blowing argon stirring are: when adding alloys to adjust the chemical composition, the bottom blowing argon flow rate is controlled at 450NL / min, and the slag surface blowing area is controlled at 150mm; during other refining times, the bottom blowing argon flow rate is controlled at 150NL / min, the slag surface moves slightly, and the bottom blowing argon flow rate exceeds 100NL / min.

[0080] Table 3 shows the specific values ​​of the soft blowing time and the ladle temperature in the LF refining operation in each embodiment.

[0081] Table 3

[0082]

[0083] (4) Continuous casting:

[0084] 1) Billet casting is carried out on an arc continuous casting machine with a billet size of 210*210mm. Tundish covering agent and mold protection slag are used to implement 100% protective casting throughout the entire process to prevent secondary oxidation of molten steel.

[0085] 2) The superheat of the first ladle is 25-40℃, and the pulling speed is 1.20m / min; the superheat of the continuous casting furnace is 20-30℃, and the pulling speed is 1.35m / min. The temperature drop of each ladle of molten steel from the beginning to the end of casting is ≤5℃.

[0086] 3) Cold water flow control 120±5m 3 / h, M-EMS electromagnetic stirring current 350A, frequency 2.5Hz, F-EMS electromagnetic stirring current 250A, frequency 10Hz.

[0087] Table 4 shows the specific values ​​of the first ladle superheat, continuous casting furnace superheat, temperature drop and cooling water flow rate in each embodiment during the continuous casting operation.

[0088] Table 4

[0089]

[0090] (5) Steel rolling:

[0091] The 210*210mm square continuous casting ingot is cold-charged into a six-heating zone walking-beam furnace. The preheating section is set at 700-800°C, the first heating section at 950±10°C, the second heating section at 1100±10°C, the third heating section at 1140±10°C, the first soaking section at 1160±10°C, and the second soaking section at 1150±10°C. The total heating time is controlled at 2.5-3.0 hours, including a high-temperature diffusion time of 1.25-1.5 hours. The starting rolling temperature is 1060-1080°C, the finishing rolling temperature is 960-980°C, the upper cooling bed temperature is 860-880°C, and the steel enters the pit for a slow cooling temperature of 435-455°C. The slow cooling time for the steel entering the pit must be 72-80 hours, and the steel surface temperature must be ≤100°C when the pit is removed.

[0092] Table 4 shows the specific values ​​of the preheating section temperature, heating section one temperature, heating section two temperature, heating section three temperature, soaking section one temperature, soaking section two temperature, and total heating time in each embodiment during the steel rolling operation.

[0093] Table 5

[0094]

[0095] Table 5 shows the specific values ​​of high-temperature diffusion time, starting rolling temperature, finishing rolling temperature, upper cooling bed temperature, slow cooling temperature of steel entering the pit, slow cooling time of steel entering the pit, and surface temperature of steel when steel enters the pit in each embodiment during the steel rolling operation.

[0096] Table 6

[0097]

[0098] The chemical compositions of the final products are shown in Tables 7 and 8 below.

[0099] Table 7 Main chemical components (wt%)

[0100]

[0101] Table 8 Residual elements (wt%)

[0102]

[0103] The mechanical properties of hot rolled steel are shown in Table 9.

[0104] Table 9 Mechanical properties of hot rolled state

[0105]

[0106] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined as such, will not be interpreted in an idealized or overly formal sense.

[0107] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for preparing high-sulfur steel for automobile wheel hubs, characterized in that: The following steps are involved: (1) Converter smelting: Non-desulfurized hot metal and high-quality scrap steel are used as raw materials for primary smelting in a converter. When tapping, silicon manganese FeMn is added in sequence. 68 Si 18 :8.5~10.5kg / t, high carbon ferromanganese FeMn 68 C 7.0 : 13~15kg / t. According to the S content requirement of the molten steel at the end of the converter, ferrosulfur is added during the tapping process to adjust the S content; Before 20 tons of steel is tapped from the converter, aluminum cakes for pre-deoxidation are added, and alloys are added after 30 tons. The alloy addition rate is controlled. When the tapping volume reaches 1 / 2, all the alloy is added to the ladle. At the same time, the bottom blowing argon stirring rate is adjusted to 500-600 NL / min. After all the alloy is melted, 3 / 4 of the slag is added. At this time, the bottom blowing argon stirring time is controlled to 1 minute. Subsequently, the bottom blowing argon stirring rate is quickly adjusted to 200-300 NL / min. The deoxidizer calcium aluminum iron is added to the impact area. After 1 minute of adding the deoxidizer calcium aluminum iron, the argon stirring rate is adjusted to 100-200 NL / min, and the remaining 1 / 4 of the slag is added to the ladle. After the slag is added, soft blowing is performed at the argon blowing station for 2-3 minutes. Aluminum wire is fed into the molten steel. 100m of aluminum wire with a specification of φ9mm is fed into the first furnace of the tundish, and 70m of aluminum wire with a specification of φ9mm is fed into the continuous casting furnace. When tapping the converter, aluminum blocks are added for precipitation deoxidation according to the oxygen determination results at the blowing end point. The slag is made by using lime, refined slag and quartz sand. The amount of lime added is 500 kg / furnace, the amount of refined slag added is 200 kg / furnace, and the amount of quartz sand added is 100 kg / furnace. (2) LF refining: 2.1) In the early stage of LF refining and when adjusting the composition, use argon blowing to stir and even the composition. Otherwise, keep soft argon blowing. The bottom blowing stirring flow rate during the refining process is less than 600NL / min; 2.2) Slag Adjustment: In principle, no additional slag is added during the LF refining process, and no desulfurization is performed intentionally. If the sulfur content of the first batch of molten steel in LF refining is too low, ferrosulfur is added to adjust the sulfur content. The refining slag must have good fluidity and the white slag time must be ≥25 minutes. 2.3) Use silicon carbide, calcium carbide, and aluminum particles to deoxidize the slag surface. The amount of calcium carbide added is 40-60 kg / furnace, and the amount of silicon carbide added is 100-120 kg / furnace. The Al content of the second sample is controlled to be 0.010%-0.015%; 2.4) Use high carbon ferrochrome to adjust the Cr content in refining; in the case of white slag in the later stage of refining, use ferrotitanium to adjust the Ti content; 2.5) No denaturation treatment is performed, and the sulfur content is fed to the sulfur line at the end of LF refining to adjust the sulfur content to the internal control range; 2.6) Soft blowing for 20 to 30 minutes; 2.7) During the refining process, the requirements for bottom blowing argon stirring are as follows: when adding alloys to adjust the chemical composition, the bottom blowing argon flow rate is controlled at 400-500 NL / min, and the slag surface blowing area is controlled at 100-200 mm; during other refining times, the bottom blowing argon flow rate is controlled at 100-200 NL / min, and it is prohibited to exceed 200 NL / min; (3) Continuous casting: The superheat of the first ladle is 25-45℃, and the casting speed is 1.20m / min; the superheat of the continuous casting furnace is 20-30℃, and the casting speed is 1.35m / min. The temperature drop of each ladle of molten steel from the beginning to the end of casting is ≤5℃; (4) Steel rolling: The continuous casting billet is cold charged into the furnace, and the walking beam heating furnace is re-divided from the original three heating zones into six heating zones; the preheating section temperature is ≤850℃, the heating section temperature is 950±10℃, the heating section temperature is 1100±10℃, the heating section temperature is 1140±10℃, the soaking section temperature is 1160±10℃, and the soaking section temperature is 1150±10℃. From the perspective of the heating area division, the preheating section, the heating section, and the heating section are the billet uniform heating sections; the heating section 3, the soaking section 1, and the soaking section 2 are the billet homogenization and high-temperature diffusion stages; the starting rolling temperature is ≥1050℃, the finishing rolling temperature is ≥950℃, the upper cooling bed temperature is ≥850℃, the slow cooling temperature of the steel entering the pit is ≥430℃, the slow cooling time of the steel entering the pit is ≥72h, and the surface temperature of the steel is ≤100℃ when the steel is out of the pit and out of the pit; The elements of the obtained steel include, in order by mass percentage, C: 0.40% to 0.43%, Si: 0.25% to 0.33%, Mn: 1.57% to 1.65%, Cr: 0.12% to 0.15%, Ti: 0.02% to 0.03%, P≤0.012%, S: 0.095% to 0.11%, Cu≤0.05%, Ni≤0.04%, As≤0.0070%, Sn≤0.005%, Pb≤0.009%, Sb≤0.0008%, Bi≤0.0005%, and the remainder is Fe and unavoidable impurity elements.

2. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, characterized in that: In the step (1), in order to prevent the molten steel from being over-oxidized, a high carbon drawing operation is adopted at the end of the converter to make the mass content of C ≥ 0.08%. When tapping, the temperature of the molten steel is 1620-1670°C, and the mass content of phosphorus in the molten steel is ≤ 0.012%.

3. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, wherein: In the step (2), argon blowing is used for stirring in the early stage of refining and when adjusting the composition to uniformize the composition. Otherwise, soft argon blowing is maintained. The bottom blowing stirring flow rate during the refining process is less than 600NL / min.

4. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, wherein: In the step (2), the temperature of the first ladle is 1557-1577°C, the temperature of the ladle in the continuous casting furnace is 1537-1567°C, the overheating degree of the first ladle is 25-45°C, and the overheating degree of the continuous casting furnace is 20-30°C.

5. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, characterized in that: In the step (3), billet casting is carried out in an arc continuous casting machine, the billet specification is 210*210mm, a tundish covering agent and a crystallizer protective slag are used, and 100% protective casting is implemented throughout the whole process to prevent secondary oxidation of the molten steel.

6. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, characterized in that: In step (3), the flow rate of cold water is controlled at 120±5m 3 / h, the M-EMS electromagnetic stirring current is 350A, the frequency is 2.5Hz, and the F-EMS electromagnetic stirring current is 250A, the frequency is 10Hz.

7. The method for preparing high-sulfur steel for automobile wheel hub according to claim 1, characterized in that: In the step (4), the square continuous casting billet is cold-charged into the furnace, and the total heating time is controlled to be 2.5 to 3.0 hours, of which the high-temperature diffusion time is 1.25 to 1.5 hours.

8. A high-sulfur steel for automobile wheel hubs produced by the method for producing high-sulfur steel for automobile wheel hubs according to any one of claims 1 to 7.

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